Question: Factor completely. $36 c ^2-121 d ^2=$
Explanation: $36 c ^2 -121 d ^2 = ({6 c })^2-({11 d })^2$ Using the difference of squares pattern: $({6 c })^2 - ({11 d })^2 =({6 c }+{11 d })({6 c }-{11 d })$ In conclusion, $36 c ^2-121 d ^2=(6 c +11 d )(6 c -11 d )$ Remember that you can always check your factorization by expanding it.